This invention relates generally to nuclear reactors, and more particularly, to containment systems in nuclear boiling water reactors.
One known boiling water reactor includes a reactor pressure vessel (RPV) positioned in a containment building or vessel, and a containment cooling system (CCS). A typical containment vessel includes both a drywell and an enclosed wetwell disposed in the containment vessel. The wetwell provides an additional source of cooling water for the reactor in the event of a pipe rupture or loss of coolant accident (LOCA). The CCS includes a passive containment cooling system (PCCS) having a heat exchanger submerged in a cooling pool located outside the containment vessel.
In the event of a LOCA, high-pressure fluid or steam is released from the RPV into the containment vessel. The steam is retained in the containment vessel, flows to PCCS and is condensed in the PCCS heat exchanger. The steam condensate collected in the condenser is returned to RPV or the containment vessel. Inside the RPV, the condensate is turned into steam by core decay heat and the steam flows back into the containment vessel. This produces a continuous process by which the reactor core is cooled by water over a period of time following the LOCA.
The containment vessel, in turn, is sized and configured to receive relatively high pressure and high temperature steam in the event of the LOCA. The containment vessel or building is typically a large volume structure made of thick reinforced concrete configured to contain a steam release. The large volume provides an expansion area for depressurization and control of the steam. The containment vessel is configured to contain low pressures, of about 2 atmospheres (atm) to about 3 atm (about 202 kilopascals (kPa) to about 303 kPa). The containment vessel also is effective as a radioactive boundary for containing the radioactive steam. Construction of the containment vessel and the support pad for the containment vessel is a complex event requiring significant time and resources at the reactor site.